Subcutaneous transmitters will be developed for chronic implantation. These will be powered by light from a light-emitting diode, and will encode physiological data for transmission as a sequence of light pulses. The goal is to develop a new technology for chronic monitoring of implanted sensors that obviates the need for percutaneous connectors. The proposed first application will be to facilitate chronic, invasive recordings for localization of epileptogenic foci. Invasive recording in preparation for ablative procedures is an accepted therapy throughout the world. Usually, patients must be kept in a hospital setting for long times while plugged into neural recording systems. One significant difficulty is the necessity for percutaneous lead wires which keep patients in the hospital. Infection and lead breakage or dislodgement are significant associated risks. A system that could transmit the brain potentials across the skin without lead wires would allow more consistent data collection from more electrode sites. This is intended to improve the chances for a beneficial outcome, lower the risk, and reduce the costs because patients could go home. The specific aim of this proposed work is to replace the percutaneous connector and lead wires of existing recording systems with an implantable, optically-linked transmitter. This biomedical signal recording and transmitter system will be self-contained and chronically implantable. It will multiplex neural potentials from 64 electrodes onto a single output channel of light pulses. By using light for transmission of data and power, rather than traditional radio frequency techniques, a system of smaller size, weight, and greater immunity to electromagnetic interference might be realized. The technology will be tested in rabbits and high-temperature soaks for long-term functionality. When sufficiently proven, test units will be attached to external leads of implanted electrodes, in parallel with existing instrumentation in the Epilepsy Center at Beth Israel-Deaconess Medical Center. When animal, saline soak, and recording tests are satisfactory, a clinical unit will be tested by implanting it in a patient undergoing invasive recording for localization of foci. Transmitting light across the skin for data and power requires pushing the limits of low noise/low power circuit design, optical power supply efficiency, and optical transmission. If successful, a new technology may be established that is power efficient, small, lightweight, and immune to electrical interference. To accomplish this design, it will be necessary to draw on expertise in solid state physics, electrical engineering, integrated circuit design and fabrication. For evaluation, expertise in neurology, electroencephalography, neurophysiology, animal models, instrumentation, and long-term implantable device packaging will be utilized. If successful, this technology might find application in the chronic monitoring of many physiological variables including temperature, pH, perfusion, oxygenation, and others.